One of the earliest in situ remedial wood treatment techniques for existing window frames comprised injection of wood preservation liquid containing 99% solvent and only 1% active compound into existing wood constructions such as window and door frames. This technique has the disadvantage of being hardly controllable and having a dubious effect.
The next method known as Woodcap comprised drilling holes and placing therein glass ampoules filled with liquid containing 95% solvent and 5% active compound and closed with a cap. By hammering or screwing the cap of the ampoule into a hole, the ampoule breaks and the contents spread.
Because this wet system suffered from leakages which are unacceptable from an environmental point of view there was a need for a dry system of wood preservation.
One known technique comprised the use of hydrophilic polymers that are able to dispense certain active compounds in a controllable manner. Such compounds have been used in predrilled holes as in the disclosed wet system.
Attempts to mould the said hydrophilic polymers into objects which can be safely handled have failed and instead a polyvinyl alcohol wrapping has been used containing a combination of the dry substance bifluoride and a hydrophilic polymer. In practice this method of wood preservation has five disadvantages. First, it needed 45% hydrophilic substance so that there was only place for 55% active compound. Second, leakage at the closing cap releases large amounts of concentrated active compound which attack paint coats. Third, it takes a long time for the active compound to dissolve. Fourth, the active compound is not homogeneously spread, and fifth, because residues of the polyvinyl alcohol accumulate in the surrounding wood the intrusion of active compound into the wood is impeded.
A more recent technique comprises the use of the active compound in the form of solid rods to be placed in pre-drilled holes.
The subject invention is based on the insight that the existing rods can be improved as far as the following aspects are concerned.
1) In order to have sufficient strength the rods need a certain minimum diameter. Because of this they are often too large for narrow window frames, which would be weakened by drilling large diameter holes therein.
2) The rods need to contain at least 45% aggregate for them to be moulded in rod form.
3) After press moulding the rods are not capillary which has an adverse effect on the dissipation of the compound into the surrounding wood.
4) For installing the rods they must be handled manually so that contact of active compound with the skin is difficult to avoid.